What are some other rigid social structures you have studied that are similar to the castas?

The correct answer to this open question is the following.

The other rigid social structures you have studied that are similar to the castas is the social class system in Medieval times in Europe or the class Pyramid of ancient Egypt.

The Castas system was developed by the Spanish people wneh they conquered the many territories in México and South America. It was a rigid system based on race and birth. The Peninsulares were people born in Spain. They were powerful and rich controlled the territories of New Spain.  The Creoles follow they were born in New Spain from Spanish parents. They owned land and businesses in the colonies. Then it came the Mestizos, people whose parents were a Native American Father and Spanish mother and vice-versa.